Maintaining data consistency in mobile computing environments

• Main Authors: Chi-Chung Lee, 李之中
• Other Authors: Yunnho Leu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/27729139718654363879

博士 === 國立臺灣科技大學 === 資訊管理系 === 92 === Data broadcast is an efficient method for disseminating data items in the mobile computing environment. With the data broadcast method, data items are broadcast periodically according to a predetermined schedule.Maintaining data consistency is an important issue in mobile computing environments. In this thesis, we study the data consistency problems in mobile computing evnironments and propose solutions for them. The first problem is on how to enable a mobile client to receive up-to-date data while the broadcast server keeps on updating the data. We call the problem that the content of a data item is not ready when it is required in a broadcast cycle the data-missing problem. To handle this problem, we revise the existing data broadcast schemes using two approaches. The reaccess approach requires a mobile client to access a missing data item in the next broadcast cycle, while the add-missing approach allows a mobile client to access a missing data item in an attached missing data segment. We compare the performance of the revised schemes in terms of access time and tuning time. The second problem is on how to use energy-efficient cache invalidation schemes to maintain data consistency between mobile clients and a database server. Query-level cache invalidation schemes were proposed to minimize the energy consumption of a mobile client in accessing the invalidation report. However, the query-level cache invalidation schemes suffer from false invalidation. False invalidation results in excessive energy consumption by requiring a mobile client to request the falsely invalidated data items in an uplink channel. To prevent the energy consumption in requesting the falsely invalidated data items, we proposed a new cache invalidation scheme. In the proposed scheme, we use index to support selective tuning for the mobile client to listen to the invalidation report. The proposed scheme uses new scale, called improved query-level, cache invalidation that minimizes the energy consumption. In the improved query-level scheme, not only the queried data items but also the non-queried data items that will become invalid in the next cycle are validated in every cache invalidation. In a performance study, we compare the improved query-level scheme with the cache-level scheme and the query-level scheme in terms of energy consumption. The result shows that the energy consumption in the query-level scheme is larger than that in the cache-level scheme and that in the improved query-level scheme.